Conventional rotary machines such as impact or attrition mills and the like suffer from the following disadvantages.
[1] Due to centrifugal force material tends to form a compacted layer on the inner periphery of the mill; PA0 [2] As a result of the condition in [1] above, excessive grinding of material producing unnecessary or excessive fines commonly takes place; PA0 [3] As a result of the condition [1] described above, difficulties are experienced in separating finer and coarser material; PA0 [4] Throughput of the mill is hampered as a result of the compaction described in [1] above and the difficulty described in [3] above; PA0 [5] Wear of certain parts of the mills is increased as a result of the conditions [2] and [3], described above.